Generally, the engine cylinder heads include intake/exhaust valves for opening and closing a passage for an air-fuel mixture flowing into a combustion chamber and exhaust gas flowing out of the combustion chamber. Theses valves each include a shaft section and an umbrella section provided at an end of the shaft section. Valve guide provided in the cylinder head has a small valve inserting hole, and thus, there is provided an extremely small gap between the shaft section and the inner surface of the valve inserting hole when the shaft section is to be inserted into the valve guide. Thus, in assembly lines, the valve insertion operation using a valve insertion apparatus and the like tends to be very difficult, and so there has been a great need for a valve insertion method and apparatus which allow the valve to be readily inserted into the valve guide.
For example, Japanese Patent Application Laid-Open Publication No. SHO-62-15032 (JP 62-015032 A) discloses a method and apparatus for inserting a valve into a valve guide by sucking in the valve. Japanese Patent Application Laid-Open Publication No. HEI-09-087043 (JP 09-087043 A) discloses vibrating a valve, and Japanese Patent Application Laid-Open Publication No. SHO-60-123323 (JP 60-123323 A) discloses a technique for inserting a desired part by vibrating the desired part.
The following lines describe the valve insertion method and apparatus disclosed in JP 62-015032 A, with reference to FIG. 6 hereof. The valve 101 is grasped by a not-shown valve grasping device so as to be moved to a position over the valve guide 102. Then, a valve sucking device 103 is abutted against a stem seal 104 mounted at the lower end of the valve guide 102, and then the valve 101 is sucked by the sucking device 103 so that the valve 101 is inserted into an opening (valve inserting hole) of the valve guide 102. After that, the valve 101 is inserted compulsorily into the valve guide 102 by means of a not-shown valve pressing unit.
FIG. 7 shows a valve burning method disclosed in JP 09-087043 A. Holes 114 and 115 are formed in upper and lower beam sections 112 and 113, respectively, which together constitute a setting jig 111. Engine valve 116 of the valve 116 is inserted into these holes 114 and 115 with an umbrella section 116 located upside. Then, during a high-temperature heating (or burning) process, the setting jig 111 is vibrated to swing a shaft section 118 of the engine valve 116, so that the engine valve 116 is prevented from remaining in a constant posture during the burning to avoid unwanted bending of the engine valve 116.
FIG. 8 shows a method disclosed in Patent Literature 3, which is designed to insert an automatic transmission spool into a valve body. Magazine having a plurality of spools inserted in advance in a plurality of holes formed therein is properly positioned relative to the valve body 132 and placed on the valve body 132. Then, the magazine 131 and valve body 132 are vibrated by a vibrator 133 so that the spools are caused, by the vibration, to move from the holes of the magazine 131 into respective inserting holes formed in the valve body 132.
However, with the valve insertion method disclosed in JP 62-015032 A and shown in FIG. 6 here, the stem seal 104 may be damaged when the valve sucking device 103 is abutted against the stem seal 104 provided at the lower end of the valve guide 102, the valve guide 102 may wear and deform by the valve sucking device 103 directly abutting against the valve guide 102 if the stem seal 104 is damaged, and a portion of the valve sucking device 103 to be abutted against the stem seal 104 may wear by being abutted against the stem seal 104 a plurality of times. Further, big sucking sound generated by the valve sucking device 103 would degrade the working environment. Further, because the valve sucking device 103 requires a sucking power source, such as a vacuum pump, the apparatus would become complicated in construction.
Further, with the method disclosed in JP 09-087043 A, where the shaft section 118 of the engine valve 116 is caused to swing by vibration during the burning in order to prevent unwanted bending of the engine valve 116, the insertion of the engine valve 116 into the valve guide tends to become difficult because there is provided no means for appropriately reducing the vibration of the shaft section 118.
Furthermore, with the insertion method disclosed in JP 60-123323 A, where the magazine 131 and valve body 132 are vibrated to cause the spools to be inserted, by their own weight, into the respective inserting holes formed in the valve body 132, any of the spools may sometimes fail to be inserted into the inserting hole in the corresponding valve body 132 due to a dimension error between the hole in the magazine 131 and the inserting hole in the valve body 132.